I don't think it was the dry heat so much as the energy expenditure from walking in deep sand and overheating from the direct sun.

From personal experience, I've found that the dry heat of the desert Southwest and eastern Columbia River Gorge is much easier to tolerate then the hot and humid climate found in south Florida. Provided, of course, that I have some shade. At 100+F in direct sun, it's like wearing my backpacking pack.
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